1. Field of the Invention
The present invention relates to a light source unit that emits a laser beam and a photoacoustic measurement apparatus using the light source unit.
2. Description of the Related Art
Photoacoustic spectroscopy is a method that includes irradiating a subject with light having a predetermined wavelength (for example, the wavelength band of visible light, near infrared light, or middle infrared light) and detecting a photoacoustic wave, which is an elastic wave generated when a specific material contained in the subject absorbs the energy of this light, to measure the concentration or distribution of the specific material (for example, JP2010-12295A). The specific material contained in the subject is glucose, hemoglobin, or the like contained in blood when the subject is, for example, a human body. Further, a technique, which detects photoacoustic waves and generates a photoacoustic image on the basis of the detected signals, is called photoacoustic imaging (PAI) or photo-acoustic tomography (PAT).
Since the intensity of a laser beam, which is applied to the subject, is significantly attenuated due to absorption or scattering while the laser beam is propagated through the subject, a laser beam having high light energy is generally used in the measurement (photoacoustic measurement) using the photoacoustic spectroscopy. As shown in, for example, FIG. 20, a photoacoustic measurement apparatus 1 includes a probe 4 for photoacoustic measurement, a light source unit 3 that supplies a laser beam L to the probe 4, and an acoustic signal processing unit 2 that processes signals of the photoacoustic waves detected by the probe 4. Further, for convenience of use, the probe 4 and the acoustic signal processing unit 2 are detachably connected to each other by a first connector 5a, and the probe 4 and the light source unit 3 are detachably connected to each other by a second connector 5b. An acoustic detecting element array 4a is provided in the probe 4, and the acoustic detecting element array 4a is connected to control means 2a of the acoustic signal processing unit 2 by a control signal line 4c. A laser beam L output from a light source 3a is guided to an end of the probe 4 by an optical fiber 4b, and a subject M is irradiated with the laser beam L.
Incidentally, when the probe and the light source unit are detachably connected to each other as described above, space transmission is frequently used without a light guide member such as an optical fiber as the transmission of a laser beam in a housing of the light source unit. The reason for this is that an optical fiber cannot withstand light energy and is broken when a laser beam is transmitted using an optical fiber in the housing. For example, the transmission of a laser beam L between the light source 3a and the second connector 5b in the light source unit 3 of FIG. 20 is performed by space transmission.